216 IN VITRO CAPACITATION OF FROZEN/THAWED STALLION SPERM

Abstract

The inability of stallion sperm to capacitate in an in vitro setting has limited many equine assisted reproductive technologies such as gamete intrafallopian transfer (GIFT) and IVF. These experiments were conducted to develop methods for artificially capacitating frozen/thawed stallion sperm, using dilauroylphosphatidylcholine (PC-12), calcium ionophore A23187 (IONO), or methyl-β-cyclodextrins (MBC) so that sperm could be used in equine assisted reproductive technologies. Assisted reproductive technologies need to be established to maximize the number of offspring produced with cryopreserved spermfrom stallions with low cryosurvival rates or that have a very limited number of frozen sperm. Low concentrations of lysophosphatidylcholine (LPC) induce the acrosome reaction in capacitated sperm and, therefore, were used to detect fully capacitated sperm treated with PC-12, IONO, or MBC. Ejaculates from 8 stallions were diluted in a modified Tyrode's medium and centrifuged (1000g for 11 min). The sperm pellets were suspended to 400 million sperm mL^–1 in EZ-Freezin LE, packaged into 0.5-mL straws, and frozen in liquid nitrogen vapor. Straws were thawed in a 37°C water bath for 30 s and washed through 35% Percoll (400g for 4.5 min) to remove egg yolk particles and seminal plasma. The sperm pellets were suspended in Medium 199 (0.6% BSA and 5 mm calcium chloride) to 50 million sperm mL^–1, and stained with propidium iodide and FITC-peanut agglutinin (PNA) (1 mg mL^–1 each; viability and acrosome reaction detection, respectively). Sperm were treated with PC-12 (13, 17, 20, 30, 40 µm), IONO (0.5, 1, 1.5, 2 µm), or MBC (0.4, 0.6, 0.8, 1 µm) and incubated in a 37°C water bath (20, 15, 20 min) to artificially capacitate sperm. Sperm were then challenged with LPC (2 or 5 µg), for 10 additional min, and analyzed by flow cytometry to determine the percentages of acrosome-reacted sperm. Data were analyzed by ANOVA and treatments were separated by Student-Newman-Keul's test. The PC-12 (20, 30, 40 µm), IONO (1.5, 2 µm), and MBC (0.4, 0.6, 0.8, 1 µm) artificially capacitated sperm equally well (59 to 70%, 52 to 59%, and 48 to 55%, respectively) and were higher than control sperm (13%, SEM ± 9; P < 0.05). Sperm viability was similar at all IONO or MBC concentrations; however, PC-12-treated sperm (17 to 40 µm) had significantly lower sperm viability when compared with control (24 to 28% and 35%, respectively, SEM ± 3; P < 0.05). In conclusion, frozen/thawed stallion sperm can be artificially capacitated by treating with PC-12, IONO, or MBC, and this may lead to practical applications for in vitro equine assisted reproductive technologies.